X-ray tubes are typically employed as X-ray sources for medical apparatuses, industrial measuring apparatuses and so forth, and have recently been employed as X-ray fluorescences (XRFs) and X-ray sources of electrostatic neutralization apparatuses, use of which has largely increased.
A typical X-ray tube includes a ceramic stem (also referred to as a vacuum tube) with cathode pins vertically disposed and an output window with a target metal deposited on its bottom surface, which are supported by ceramic valves and soldered to each other, and focusing electrodes are disposed along an inner circumferential surface of the ceramic valve simultaneously while lower portions of the focusing electrodes are fitted with the ceramic stem by means of valves. That is, the ceramic components are used at two points, and thus the components must be handled with care. In addition, it is difficult to manufacture the X-ray tube at a low cost. Both the stem and the output window need to be soldered, and thus manufacture thereof is very time-consuming. In addition, the X-ray tube usually requires different soldering materials for both the stem and the output window so that the operation process becomes complicated, which makes mass production difficult. In addition, a process of soldering the output window and the ceramic valve is carried out after a process of mounting a tungsten coil (i.e., a cathode filament) on the cathode pins. Accordingly, the tungsten coil and the cathode pins where the tungsten coil is fixed are exposed to a high temperature and the fixing portion for the tungsten coil and the cathode pins is heated. As a result, the fixing portion between the tungsten coil and the cathode pins becomes loose, which leads to deterioration of properties and lifetime of the filament so that the reliability may be lost.
Meanwhile, a conventional thermionic emission X-ray tube using filaments usually employs a diode structure of a cathode and an anode. To detail this, it employs a technique of applying a high voltage to the anode to accelerate electrons when the electrons are emitted from the cathode, which thus makes it difficult to focus and control the electrons. Further, since the thermionic emission from the filament is omni-directional, the efficiency with regard to an amount of electrons actually reaching the anode becomes extremely low.
To cope with such a problem, one of the materials recently in the limelight is a nano emitter. The nano emitter acts as an emitter using a field emission principle that electrons are emitted when an electric field is applied to a pointed conductive emitter in a vacuum state, and provides the most superior performance and very high efficiency since it has unidirectional linearity of electron emission.
FIGS. 1A and 1B illustrate a conventional X-ray tube using nano emitters. FIG. 1A illustrates a transmissive type structure and FIG. 1B illustrates a reflective type structure.
Referring to FIGS. 1A and 1B, according to the conventional X-ray tube using nano emitters, when electrons are emitted from nano emitters 110 formed in a cathode 120 according to the electron emission induction of a gate 130, the emitted electrons are focused onto anodes 140a and 140b by focusing electrodes E, which then collide with the transmissive type anode 140a or the reflective type anode 140b to generate an X-ray (L). That is, the gate 130 for inducing the electron emission is disposed between the transmissive type anode 140a and the cathode 120 or between the reflective type anode 140b and the cathode 120, and thus the triode structure is implemented.
However, according to the conventional X-ray tube using nano emitters, focusing the electron beams is adjusted by the voltage to be applied to the focusing electrodes E, so that another separate focusing electrode E must be disposed when the electron beam focusing needs to be implemented or enhanced, which thus results in a complicated structure and a difficult manufacturing process.
Further, when the electrons Bleak emitted from nano emitters 110 are leaked to the gate 130, the gate 130 is deformed due to thermal deformation or the like resulting from the leakage current so that the reliability of the electron emission is lowered, which must also be necessarily overcome.
In a case of the XRF, when a high voltage of about 40 kV is applied to the anodes 140a and 140b for accelerating electrons, the structure may be damaged due to undesired arcing or the like, which must also be overcome.